Skeletal Tissue PDF

Bone Osseous Tissue and Bone Structure Skeletal Functions Support Protection Mineral& Lipid Storage Blood Cell Production Leverage/Movement/Anchorage Bone Classification Bone shape – Long bones-long & slender – Short bones-boxy – Flat bones-thin – Irregular bones-odd shaped – S...

Bone Osseous Tissue and Bone Structure Skeletal Functions Support Protection Mineral& Lipid Storage Blood Cell Production Leverage/Movement/Anchorage Bone Classification Bone shape – Long bones-long & slender – Short bones-boxy – Flat bones-thin – Irregular bones-odd shaped – Sesamoid bones-form in tendons – Sutural bones-skull bones Bone Structure Diaphysis – Shaft of the bone Epiphysis – Expanded ends Metaphysis – Site where diaphysis & epiphysis meet Bone Histology Bone contains cells and osteoid Cells form in lacunae, organized by blood vessels Canaliculi form branches of blood vessels for exchange of materials Covered by periosteum  Bone matrix is 55% crystalized mineral salts; 30% collagen & 15% H2O – Most abundant is calcium phosphate, which interacts with calcium hydroxide to form hydroxyapatite – Interact with calcium carbonate, Na+, K+, Mg++, & Fl- “Hardness” is based on mineral salts, “flexibility” is based on collagen Bone Cells Osteocytes – Mature bone cells that exist in a lacunae covered by layers of matrix, lamellae – Non-dividing cells – Maintain mineral content of matrix – Helps repair damaged bone  Osteoprogenitor/Osteogenic Cells – Stem cells that differentiate into osteoblasts – Found in periosteum, endosteum & in canals Osteoblasts – Produce/build new bone via osteogenesis – Eventually produce osteocytes  Osteoclasts – Destroy/carve out bone material & release minerals – From monocytes – When production is faster that that of osteoblasts…bones weaken – When production decreases, bone strengthens  Bone Structure – Osseous tissue has 2 forms Compact bone – Dense/solid bone – Forms Osteons Spongy bone – Open network – Cancellous bone forms Trabeculae Compact Bone Functional units are osteons which form concentric rings around a central canal (Haversian) which contains blood vessels Perforating canals (Volkmann) connect osteons  Stresses from fewer angles increase compact bone’s density Osteons are like long, thin straws that travel the length of bone, parallel to one another Bone is very strong in the long axis, but less so in the perpendicular direction Spongy Bone Forms “struts & plates” called trabeculae, a mesh-like network – Form where less stress occurs – Reduces weight of bones Protects bone marrow – Yellow Marrow Fatty, offers backup energy reserves – Red Marrow Mature & immature RBC’s, WBC’s & stem cells Important for blood cell formation Periosteum Superficial layer covering the bone – Separates bone from other tissues – Provides circulatory & nervous system routes – Assists in bone growth & repair Continuous with other CT’s like tendon, joint capsules, etc As bone grows, tendons cement to the bone Endosteum Thin vascular membrane – Lines the marrow cavity Made of osteoprogenitor cells Works with growth, repair & remodeling Reabsorbed during times of malnutrition Development & Growth Bone growth begins at 6 weeks (as an embryo) and continues until 21-25 years Ossification & Calcification occur in 2 ways – Endochondral Ossification – Intramembranous Ossification Endochondral Ossification Begins with Hyaline Cartilage – Cartilage enlarges/chondrocytes increase – Blood vessels grow near & perichondrium cells become osteoblasts – Blood vessels penetrate cartilage in the diaphysis & then cells differentiate into osteoblasts to create spongy bone in the primary ossification center Bone growth occurs in an outside TO inside direction along the diaphysis – Remodeling of trabeculae occurs and osteoclasts form the marrow cavity – Secondary ossification centers form in each epiphysis (around birth) Spongy bone remains; no marrow cavities Grows from inside TO outside – Growth plates occur between the diaphysis and epiphyses at the metaphysis (AKA the epiphyseal cartilage/plate)  Puberty & sex hormones  bone growth – Eventually growth plates disappear Appositional bone growth occurs as the bone widens in circumference – Outer layers added as inner layers are removed Interstitial bone growth occurs as the bone lengthens Intramembranous Ossification From Fibrous CT & Mesenchyme cells Flat bones like the skull, facial bones & mandible, and parts of clavicles – Mesenchyme cells become clusters of osteogenic cells – Forms trabeculae with a thin “layer” of compact bone on the surfaces Blood & Nervous Supply 3 major sets of vessels – Nutrient artery & vein – Metaphyseal vessels – Periosteal vessels Periosteum also has lymphatic vessels Nerves enter endosteum, marrow & epiphyses Bone Remodeling Bone is continuously turned over – Activity of osteocytes, osteoblasts & osteoclasts should be balanced InTeens & Twenties: 20% of bone material is remodeled…slows as you age Spongy bone has much greater turnover (20%) than compact bone (5%) Exercise When bone is stressed, tiny electrical fields occur which attracts osteoblasts Bone markings form via pulling from muscles Exercise increases bone thickness, while the absence of it thins bone – Inactivity quickly reduces bone mass – A few weeks after an injury 1/3rd of bone mass may be lost – Astronauts lose 1% a week – Importance of rehab after injury Nutrition Calcium required (Mg, Fl, Fe, & Mn) Vitamin D, which works with the hormone calcitriol to absorb Ca Vitamins A, K, C, B12 Growth Hormone, Thyroxine (T4), estrogens & androgens control bone growth Calcitonin & PTH Skeletal Reserves 2-4 lbs of calcium, 99% in bones – If Ca+ in blood increases by 30%, muscles become unresponsive – If it decreases over 30%, convulsions may occur – Over 50%, causes death (often cardiac failure) Daily fluctuations stay within 10% Fracture Repair Step 1—bleeding occurs and a clot/ hematoma occurs and osteocytes die off near the injury Step 2—an external callus forms from the periosteum & and an internal callus forms via the endosteum. Chondrocytes differentiate into osteoblasts  Step 3—Osteoblasts replace cartilage with spongy bone while dead bone gets removed Step 4—Osteoclasts & osteoblasts con- tinue the repair cycle for up to a year. The callus eventually is removed. Bone may be thicker at the site of fracture Types of Fractures Open – AKA Compound – Project through the skin Closed – AKA Simple – Completely internal https://www.youtube.com/watch?v=qoiaUV7fGEI https://www.youtube.com/watch?v=Z7acc6qwcmQ  Complete – Bone fragments separate Incomplete – Bone fragments still joined Based on Direction: – Linear – Transverse – Oblique  Spiral Fractures – Due to twisting stresses Compression Fractures – Usually vertebral; due to extreme stress Comminuted Fractures – Shatters into many pieces Compacted/Impacted – Ends of bones driven into each other  Greenstick – Occurs with a bend Epiphyseal – At epiphyseal plate. Clean breaks heal well; jagged do not Pathologic – Disease process weakens the bones Avulsion – Muscle tears a piece off of the bone Aging Osteopenia – Occurs with inadequate ossification – Bone mass begins to decrease in your 30’s – Women lose 8% a year & males 3% Osteoporosis – When function becomes compromised – 24.5% of women & 5.1% of men > 65 yrs – May be a secondary effect of bone cancers – Usually treat with antireabsorptive drugs Risk Factors: – Age – Lifestyle (diet, where Risk  after mid-30s you live & exercise) – Race – Smokers Caucasian, Asian, – Alcoholics Mexican-American – Eating disorders – Height & Weight – GI Sx Being >5’ 7” tall or weighing